The present disclosure relates generally to the movement of loads and, more particularly, to the measurement and control of sway in load transportation systems.
Load transportation systems such as ship-to-shore cranes, tower cranes, marine-based cranes, Rail-Mounted Gantry Cranes (RMGC), and boom cranes are often used to move loads from one location to another. These loads are often large and heavy and tend to sway or swing during movement. Load sway decreases transportation efficiency and increases the risk of damage and injury.
An example of a typical load transportation system 100 is shown in FIG. 1. The system 100 may comprise, for example, a load spreader 102 suspended from a trolley 104 by one or more trolley ropes 106. For example, where the load 108 is a rectangular box container, a trolley rope 106 may support each of the four top corners of the load spreader 102 carrying the container 108.
The trolley 104 may travel along a rail 110 which may be the rail of a crane. For example, the rail 110 may be a standard “I” beam or steel “W” section and/or the load jib of a tower crane. The trolley 104 may have one or more pulleys 112 that may be used to raise or lower the load spreader 102 and any load 108 carried by the load spreader 102.
When the load 108 is transported from one location to another the load 108 may sway. In the system 100 shown in FIG. 1 the sway may be defined, for example, as the deviation of the load 108 from the position expected of the load 108 at rest. The magnitude and/or direction of sway may change, sometimes frequently, such as when the load 108 swings beneath the trolley 104. The sway may be dictated by various factors including, but not limited to, the weight and/or configuration of the load 108, the length of the trolley ropes 106, the speed and/or motion of the trolley 104, and/or various weather conditions such as prevailing winds, or wave motions affecting marine-based cranes.
The sway of the load 108 must generally be monitored and/or controlled to avoid collisions or damage to the load and/or to increase load transportation efficiency. For example, the sway may often need to be minimized to allow the crane operator to easily place the load 108 in a desired location with a high degree of precision (often measured in centimeters). Unfortunately, current methods of controlling the sway are often limited to reliance upon a skilled operator to minimize sway and efficiently transport the load 108.
Electronic systems for reducing sway (such as shown in FIG. 1) typically consist of a camera 114 mounted on the trolley 104 and a reflector 116 mounted on the load spreader 102. The camera 114 records images directly beneath the camera 114 including the position of the reflector 116. The images may then be interpreted to determine the sway of the load. Lights 118 may be used to illuminate the area beneath the camera 114 to facilitate viewing of the reflector 116. The reflector 116 may also be heated to reduce condensation and/or other weather-related effects that could inhibit visibility.
Unfortunately, such systems are often costly and inefficient, requiring expensive cameras, complicated reflector mechanisms, high-intensity lights, and taxing image interpretations (either manual or using powerful computer processors) to determine sway. Further, such costly components may often fail, contributing to increased maintenance costs of such systems.
Accordingly, there is a need for sway control that addresses these and other problems found in existing technologies.